Clutch with dissimilar frictional facings and centrifugal assist

ABSTRACT

There is disclosed an automotive clutch in which frictional engagement faces of a clutch are provided with an organic composite facing and a sintered metal facing. By this combination, the benefits of both types of facings are obtained without any of the disadvantages that formerly plagued the use of these facings. In the invention, the organic composite facing provides the low temperature service for the clutch with a suitably high coefficient of friction which is relatively constant from ambient to several hundred degrees F. The sintered metal facing provides high temperature service for the clutch. Thus, when the organic composite facings reach their maximum service temperature of around 500 degrees F., the sintered metal facings provide their optimum coefficient of friction, resulting in a subassembly in which the overall or average coefficient of friction remains substantially constant from ambient temperatures to the maximum service temperature of the sintered metal coatings, in excess of 900 degrees F. The result, when incorporated in an automotive clutch, is a clutch having a very smooth, non-vibrational action which does not exhibit premature wear and failure.

RELATIONSHIP TO OTHER APPLICATIONS

This application is a continuation-in-part of my copending application,Ser. No. 301,439, filed Jan. 25, 1989, now U.S. Pat. No. 4,951,793.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to improvements in automotive clutches and, inparticular, to a clutch with improved frictional facings.

2. Brief Statement of the Prior Art

In most automotive and truck vehicles, torque is transmitted to thedrive shaft through a clutch disc which is mounted on the transmissioninput shaft and which is received between a pressure plate of the clutchand the flywheel. Resilient springs, either coil springs or a Bellvillespring, apply a resilient force to the pressure plate to bias it towardsthe flywheel, frictionally securing the clutch disc between the pressureplate and the flywheel, and a lever mechanism is provided to release thespring force and retract the pressure plate to disengage the clutch.

Asbestos facings have been used for many years and have served suitablyas frictional facings on the surfaces of the clutch disc. These facingshowever, have fallen into disfavor because of the health hazardpresented by asbestos, and recent attention has focused on alternativematerials. Of these alternative facings, the most commonly used havebeen organic, and/or composite, facings. The composite facings areformed of carbon or various resins which are reinforced with non-toxicfibrous materials, and are commonly referred to as organic composites,although in some instances they are formed of carbon rather than organicmaterials. As used hereinafter, these will be referred to as organiccomposite facings and this term is intended to include all carbon andorganic facings.

A difficulty with the organic composite facings is that they areentirely unsuited for use at high temperatures. The coefficient offriction of the organic composite materials declines dramatically atelevated temperatures, typically at temperatures in excess of 500degrees F. These temperatures can be quickly achieved on the surfaces ofthe frictional facings of a clutch, particularly if there is anexcessive amount of sliding movement of the members during clutchengagement. This results in an accelerated failure since as thetemperature increases, the coefficient of friction decreases, causingmore slippage and frictional rubbing of the surfaces, which furtherincreases the temperature, resulting in premature wear and destructionof the surface. Often the organic composite facings are damaged by apermanent surface glazing, which results from overheating of the clutch.When this occurs, the facing looses its original frictional propertiesand significantly deteriorates in performance.

In severe, high usage commercial applications, sintered metal facingsare commonly used. These sintered metal facings are frequently providedas a friction facing in the form of a disc, or individual pucks, whichare generally trapezoidal shaped members that are bonded or secured withfasteners to the surfaces of the clutch disc, pressure plate, orflywheel. The sintered metal facings have very low coefficients offriction at low and ambient temperatures. At temperatures in excess ofseveral hundred degrees F., however, the sintered metal facings exhibitvery acceptable coefficients of friction.

Attempts have been made to adapt the sintered metal facings to clutchmembers for normal automotive applications, however, these attempts havenot been successful, primarily because of their abrupt, uncontrollablecharacteristics and because they are two to three times as heavy asorganic composite facings. Their greater weight creates excess inertialoading resulting in excess wear of transmission components. In fact,one noted automotive authority, Mr. Thomas Monroe, has written thatsintered metal facings are entirely unsuited for normal automotive useand will never be used in normal applications, Clutch and FlywheelHandbook p 66 (1987). The greater weight of sintered metal facings andtheir low coefficient of friction values at normal operatingtemperatures results in vibration, slipping, chattering and prematurewear of the clutch.

OBJECTIVES OF THE INVENTION

It is an objective of this invention to provide an improved frictionalplate subassembly.

It is further an object of this invention to provide a frictional plateassembly with extended low and high temperature frictionalcharacteristics which are substantially constant throughout the completetemperature range.

It is also an object of this invention to provide a frictional plateassembly which is free of all objectionable environmental and healthconcerns.

It is also an object of this invention to provide a frictional plateassembly which provides for smooth efficient clutch operation andsuperior engagement control by the operator.

It is a further object of this invention to provide the aforementionedfrictional plate subassembly for use in a clutch of an automobile, truckor similar vehicle.

It is also an object of this invention to provide an improved automotiveclutch which is highly suitable for severe and heavy use, such asexperienced by commercial and competitive vehicles.

It is also an object of this invention to provide a clutch with superiorfrictional characteristics which can successfully operate with reducedfrictional surface area, resulting in smaller clutch assemblies andcomponents.

It is also an object of this invention to provide a clutch which willoperate efficiently using less total clamping pressure, therebyproviding longer engine and bearing life, reduced clutch component wear,and less operator fatigue.

It is also an object of this invention to provide a clutch which willoperate at lower temperatures than present clutches, thereby reducingclutch component damage or failure.

It is also an object of this invention to provide a clutch which canutilize some organic composite facings such as the very lightweight"carbon-carbon" materials which reduces disc inertia, therebyfacilitating disc release and providing easier transmission shifting andincreased transmission component life.

BRIEF DESCRIPTION OF THE INVENTION

This invention comprises the combination of organic composite organicfacings and sintered metal facings in a single frictional assembly. Itis specifically applied to an automotive clutch in which frictionalengagement faces of a clutch are provided with an organic compositefacing and a sintered metal facing. By this combination, the benefits ofboth types of facings are obtained without any of the disadvantages thatformerly plagued the use of these facings. In the invention, the organiccomposite facing provides the low temperature service for the clutchwith a suitably high coefficient of friction which is relativelyconstant from ambient to several hundred degrees F. The sintered metalfacings provide high temperature service for the subassembly. Thus, whenthe organic composite facings reach their maximum service temperature ofaround 500 degrees F., the sintered metal facings provide their optimumcoefficient of friction, resulting in a subassembly in which the overallor average coefficient of friction remains substantially constant fromambient temperatures to the maximum service temperature of the sinteredmetal coatings of 900-1800 degrees F. The result, when incorporated inan automotive clutch, is a clutch having a very smooth, non-vibrationalaction which does not exhibit premature wear and failure.

In its most preferred application, a clutch disc with the differentfacings, as described above, is combined in an assembly having improvedcentrifugal weights that provide a centrifugal assist to the conicalspring diaphragm type clutch cover assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the Figures of which:

FIG. 1 is an elevational sectional view of a typical automotive clutchwhich utilizes the frictional facings of this invention;

FIG. 2 is a plan view of an improved clutch disc for use in theinvention;

FIG. 3 is an elevational view of the clutch of FIG. 2;

FIG. 4 is a graph illustrating the coefficients of friction of organiccomposite and sintered metal facings as a function of temperature;

FIG. 5 is a graph of the torque transmitted by the organic composite andsintered metal facings, separately and jointly, as a function oftemperature;

FIG. 6 is a sectional elevational view of a clutch assembly with aclutch disc having both metallic and composite organic facings and acentrifugal assisted spring diaphragm; and

FIG. 7 is a plan view of a portion of the clutch assembly of FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to FIG. 1, a conventional clutch cover and flywheelassembly is illustrated in cross sectional view. The particular assemblywhich is illustrated has a diaphragm pressure plate, however, theinvention is equally applicable to other pressure plate designs such asthose using levers and compression coil springs, rather than theillustrated diaphragm.

The clutch cover 20 is secured to the flywheel 30 by a plurality ofscrew fasteners 32 which are received in internally threaded bores 34 inthe flywheel. The pressure plate 40 has a flat undersurface 42 whichengages the clutch disc 50 and applies pressure thereto, frictionallysecuring the disc 50 between the engaging surface 42 of the pressureplate and the engaging surface 36 of the flywheel. The opposed,frictional bearing surfaces are covered with a frictional material. Inthis invention, an organic composite facing 43 is provided between thepressure plate and the clutch disc 50, and a sintered metal facing 45 isprovided between the flywheel and the clutch disc 50.

A plurality of bosses 24 are peripherally disposed about the cover 20and receive machine bolts 26 which maintain retractor clips 60 in theassembly. Cover 20 has a generally flat annular land 28 which has aplurality of spaced apart apertures that receive fasteners such asrivets 61 which retain the upper pivot ring 62 and the lower pivot ring64 for the Bellville diaphragm 66. The peripheral edge of the Bellvillediaphragm 66 engages the upstanding edge 48 on the upper face of thepressure plate 40.

The pressure plate 40 is secured in the assembly by drive straps (notshown) which extend between the underside of the cover 20 and thepressure plate 40, thereby rotationally interlocking these members,while permitting relative axial movement. The retractor clips 60 arespaced equally about the periphery of the pressure ring on the upperends of bosses 24 and the inside ends of the clips hook over the top ofthe Bellville diaphragm 66, interlocking the peripheral edge of thediaphragm to the pressure ring so that an upward flexing of thisperipheral edge (which occurs when the diaphragm is compressed) retractsthe pressure plate from the disc 50.

Referring now to FIG. 2, the subassembly of the clutch disc 50 andfacings 43 and 45 is shown in an exploded view. The organic compositefacing 43 is shown in plan view in FIG. 2. The sintered metal facing 45,which is shown in FIG. 3 is on the underside of the disc as it appearsin FIG. 2, and it has essentially the same, continuous planar surface asthe illustrated organic composite facing 43. The organic compositefacing 43 and the sintered metal facing 45 can be provided in anycombination in the clutch assembly, either on the flywheel, pressureplate or clutch disc. In the preferred and illustrated embodiment, thesetwo facings are applied to opposite sides of the clutch disc.

One advantage of the invention is that each surface of the clutch disccan be provided with the frictional facing best suited for theparticular application. Thus, when a nodular iron flywheel is used, themetallic facings are applied to the side of the clutch which engagesagainst the flywheel, and the organic composite facing is applied to thepressure plate side of the clutch disc. This insures minimum temperaturerise with the clutch since the large mass and excellent heatconductivity of the flywheel minimizes thermal effects. When, however,an aluminum flywheel is encountered, it is preferably to locate theorganic composite facing on the side of the disc which engages thealuminum flywheel to minimize wear on the flywheel. The metallic facingin this application will be applied to the pressure plate side of theclutch disc.

Each facing, 43 and 45, is formed as a flat circular disc 57 with acentral aperture 59 of sufficient diameter to be received over thecentral area of the assembly which contains the torsion dampermechanism. Each disc has a plurality of small diameter through apertures41 which are counterbored to receive conventional rivets 45 which aresunk in the counterbores and which secure the facings to the clutchdisc. Alternatively, the facings can also be secured to the opposingface of the clutch disc by other conventional means, such as by bondingwith cement, silver solder, welding, etc. Also, other mechanicalfasteners such as machine screws and the like can be used.

The clutch disc 50 can be any of the various conventional clutch discs,and can include any of the various single or multiple stage torsiondamper mechanisms, and any of the various mechanisms for cushiondeflection, such as single-segment cushion, double-segment cushion,cushion plate, intermediate plate cushion, etc. Typically, the disc hasa hub 51 which has a splined aperture 53 which is received over the endof the transmission shaft (not shown). The hub 51 extends from a hubflange 67 which has a cover plate 55 with a plurality of spacer bolts(or rivets) 63 to retain the hub assembly. The hub flange and coverplate have a plurality of aligned slots 71 which receive compressioncoil springs 75. Upwardly folded flanges 69 extend along each slot 71and serve as spring retainers. The springs 75 are also received inaligned apertures in the clutch plate, or segments, depending on theclutch design. This provides a resilient mechanical link between the hub51 and the clutch plate.

The clutch is illustrated in FIG. 3 with a single-segment cushionstructure, in which the facings 43 and 45 are riveted to a segmentedplate 73 with a plurality of segments 74 which are formed with a slightconvolution, thereby providing resiliency to axial loading andcompression.

The sintered metal facing 45 can be formed integrally of sintered metalusing conventional powdered metal technology. Common materials for thesintered metal facing can be bronze, aluminum alloys, steel alloys, etc.In most conventional automotive applications, the clutch disc has adiameter from about 6 to about 12 inches. Typically, the segments whichform the clutch disc are from about 1/16 to about 3/8 inch thickness,and the frictional surfaces have adequate thickness, usually from 1/8 toabout 3/8 inch, to provide adequate life. A suitable material for thisapplication is available under No. 988-2A from Friction ProductsCompany, 920 Lake Road, Medina, Ohio 44256-3503.

The organic composite facing 43 is commonly formed as a circular dischaving a thickness typically from about 1/8 to about 1/4 inch and isformed of carbon, graphite, or thermosetting organic resins such aspolyamides, urea formaldehyde, polyimides, polysulfides, etc., and areusually reinforced with fibrous materials such as chopped fiberglass,graphite fibers and the like. A facing material which can also be usedis available under the designation: Carbon-Carbon, from HITCO, Gardena,Calif. This facing has a very high density carbon, with excellent wearand frictional properties. It has a porous carbon structure, and has notgenerally been used in automotive applications because this service istoo severe. It is desirable, however, as it reduces the inertia on theclutch disc and thus, reduces the wear on the transmission. It can beused as the organic composite facing in this invention, as the sinteredmetal facing substantially reduces the severity of the wear which isnormally experienced when only organic composite facings are used.Another suitable facing is available under the designation: VGL LOCKfrom the Ray Mark Corporation, Manheim, Pa.

FIG. 4 illustrates the temperature effects on the coefficients offriction of a typical organic composite facing shown by curve 80 and ofa typical sintered metal facing shown by curve 82. These curves werederived from the manufacturers' technical performance data for thefacings.

The coefficient of friction of the organic composite facing increasesslightly from a value of about 0.25 at ambient temperature to a highvalue of about 0.37 at 500 degrees F., and then rapidly declines attemperatures in excess of 500 degrees F. The coefficient of friction ofthe sintered metal facing (curve 82) is low at ambient temperature,about 0.1. It rapidly increases as the temperature rises to 200 degreesF. and then slowly continues to rise with increasing temperature,reaching a maximum value of about 0.83 at about 500 degrees F. Althoughthe coefficient of friction declines slightly above 500 degrees F., therate of decline is slight, and the value of the coefficient remainsconsistently high at temperatures up to 900 degrees F., and greater.

The average coefficient of friction for both facings is shown by thecurve 84. It follows the contour of the sintered metal facing 82.

FIG. 5 illustrates the torque transmitted through a typical clutchhaving facings with an outside diameter of 10.4 inches, an insidediameter of 6.5 inches and with a pressure force of 2000 pounds. Curve90 illustrates the torque transmitted by the clutch with only organiccomposite facings, curve 92 illustrates the transmitted torque with onlysintered metal facings, and curve 94 illustrates the torque transmittedwith both organic composite and sintered metal facings. From thesecurves, it is apparent that the combined organic composite and sinteredmetal facings provides superior performance, as the transmitted torquefor the combination is significantly greater than for either facing,used alone. The superiority of the combined facings over the sinteredmetal facings at the low temperature range is readily apparent, for thecombined facings transmit much greater torque at temperatures fromambient to about 450 degrees F., and only above 500 degrees F. does thecurve for transmitted torque of the combination (line 94) converge onthat for the sintered metal facings, alone (line 92). It is also readilyapparent that the organic composite facings begin to fail attemperatures of 400 degrees F.

FIGS. 6 and 7 illustrate a clutch disc 50 which is surfaced with ametallic facing 45 which engages against the flywheel 30 and an organiccomposite facing 43 which engages against the pressure plate 40. In thisillustration, the clutch assembly is provided with centrifugal weights108 for a centrifugal assist to the diaphragm spring 66. Thiscentrifugal weight assist is the subject of my prior U.S. Pat. No.4,425,991. As shown in FIG. 7, a plurality of sliding weights 108 aremounted on diaphragm 66, one each in each of the slots 67 of thediaphragm. The weights 108 are interconnected by a spring wirediscontinuous loop 117 which is passed through apertures 111 in theshanks of weights 108. Wire ring 119 is laid on the diaphragm 66,encircling the assembly of weights 108 and loop 117. Ring 119 is spotwelded at 121 to the diaphragm 66, thereby preventing weights 108 frommoving into interference with the inner edge of cover 50. The assemblyas shown in FIGS. 6 and 7 provides a centrifugal loading or assist tothe conical spring diaphragm 66, with the following advantages. Themodified clutch will not lock in the disengaged position by overcentering of the conical spring diaphragm, since any tendency for thediaphragm to move to an over-centered position will be overcome by thecentrifugal weights. The pressure loading of the assembly increasesdramatically with increasing engine speed so that the clutch coverassembly can be utilized at a wide range of engine speeds. Thecentrifugal forces develop evenly across the entire surface of thespring diaphragm, insuring against warpage or uneven loading.

The organic composite facing 43 provides smoothness in shifting andavoids the vibration and chattering which is characteristic of thesintered metal facings at low temperatures, while the sintered metalfacing provides high temperature service, insuring that the clutchperformance does not deteriorate as the service temperature increase.

The use of the two, dissimilar friction facings on the clutch discinsure that the clutch can be engaged smoothly without damage andwithout the chatter which characterizes the operation of discs with onlymetallic facings. When the clutch disc is combined with the centrifugalweight assist, the result is a clutch which can be used at very highspeeds, and under greatly increased loading, while preserving all thesmoothness and ease of shifting desired for street use.

The combination of a sintered metal facing and a organic compositefacing was installed in a 1986 Chevrolet S-10 short bed truck having a2.5 liter displacement, four cylinder engine. The clutch was thestandard original equipment of the vehicle with a clutch disc outsidediameter of 9.125 inches and a pressure plate force of 1100 pounds. Themetal facing was applied on the flywheel side and the organic compositefacing was applied on the pressure plate side of the clutch disc. Theclutch performed smoothly without any chatter or vibration. After 3000miles, the clutch was disassembled and inspected, and it was observedthat only minimal wear had occurred as there was no measurable decreasein the thicknesses of the facings and the lathe machining marks werestill visible on the pressure plate. Similar observations were made whenthe combination of the sintered metal and organic composite facings wereinstalled on a 1984 Toyota Celica ST with a 2389 cubic centimeterdisplacement engine and the manufacturer's standard clutch having a 225millimeter outside diameter clutch disc with a pressure plate force of945 pounds. The clutch fitted with the facings in accordance with thisinvention performed smoothly with no vibration or chattering.

When sintered metal facings are applied to both sides of the clutchdiscs of the above-identified vehicles, the clutches chatter andvibrate, and the clutch operation becomes uncontrollable.

The invention has been described with reference to the illustrated andpresently preferred embodiment. It is not intended that the invention beunduly limited by this disclosure of the presently preferred embodiment.Instead, it is intended that the invention be defined, by the means, andtheir obvious equivalents, set forth in the following claims:

What is claimed is:
 1. A clutch assembly wherein a clutch disc havingfirst and second planar faces is clamped between a flywheel and apressure plate, each having a respective face contiguous to and opposingone of said first and second planar faces of said clutch disc andincluding a conical diaphragm spring having a plurality of radialfingers for engagement with a clutch release bearing, to rotationallysecure said clutch disc between said flywheel and said pressure plate,whereby said plate assembly moves as a single assembly, and fulcrummeans annularly spaced about said conical diaphragm spring wherebycompression of said conical diaphragm spring releases pressure on saidpressure plate, the improvement comprising:a. an organic composite,frictional facing and no sintered metal facing on a first side of saidclutch disc; and b. a sintered metal frictional facing and no organiccomposite frictional facing on the other side of said clutch disc; c. aplurality of weight means evenly spaced about said diaphragm spring andmechanically interlocked to the fingers thereof to develop a centrifugalforce upon rotation of said clutch and urge the conical extension ofsaid diaphragm spring.
 2. The frictional plate assembly of claim 1wherein said clutch disc has a center hub with a splined aperture to bereceived over a transmission shaft of a motor vehicle.
 3. The frictionalplate assembly of claim 2 wherein said organic composite, frictionalfacing has a coefficient of friction which decreases at temperaturesabout 500 degrees F.
 4. The frictional plate assembly of claim 3 whereinsaid sintered metal frictional facing has a coefficient of frictionwhich increases to a maximum value at about 500 degrees F. and remainssubstantially constant at more elevated temperatures.
 5. In a clutchassembly of a clutch disc received between a pressure plate and aflywheel with the surface of said pressure plate and flywheel opposed tocontiguous surfaces of said clutch disc to provide a first set ofsurfaces comprising a surface of said clutch disc and an opposed surfaceof said pressure plate, and a second set of surfaces comprising theopposite surface of said clutch disc and the opposed surface of saidflywheel, and including a conical diaphragm spring bearing against andapplying compression to said pressure plate and having a plurality ofradial fingers for engagement with a clutch release bearing, fulcrummeans annularly spaced about said conical diaphragm spring, wherebycompression of said diaphragm spring release pressure on said pressureplate, the improvement comprising:c. an organic composite, frictionalfacing and no sintered metal facing on said first set of surfaces; d. asintered metal frictional facing and no organic composite frictionalfacing on said second set of surfaces and c. a plurality of weightsevenly distributed across the surface of said conical diaphragm springand mechanically interlocked to said spring to apply a centrifugal forceto said spring upon rotation of said assembly and thereby increase saidcompression on said pressure plate.
 6. The clutch assembly of claim 5wherein said clutch disc has a center hub with a splined aperture to bereceived over a shaft.
 7. The frictional plate assembly of claim 5wherein said organic composite, frictional facing has a coefficient offriction which decreases at temperatures above 500 degrees F.
 8. Thefrictional plate assembly of claim 7 wherein said sintered metalfrictional facing has a coefficient of friction which increases to amaximum value at about 500 degrees F. and remains substantially constantat more elevated temperatures.